HSC (presumed to stand for Hannes Seifert Composition) is an audio format that stores instructions for a sound card equipped with an OPL2 (AdLib, Sound Blaster, etc.). The format was designed, programmed, and implemented by Hannes Seifert. Seifert used this format in several of the games he helped develop in the mid-1990s.

In 1994, the demogroup Electronic Rats (ECR) reverse-engineered the format and player and also built an editor for them, called HSC-Tracker. This caused the format to become especially popular. At some point, Number Six / Aegis Corp. created a compressed version of the format called HSC Packed which uses the extension *.hsp.